The present invention relates to an apparatus for the compaction of foundry mold making material using gas under pressure and made up of a pressure vessel forming an inlet space or initial pressure stage for the gas under pressure, a mold chamber placed thereunder and formed by a mold flask with a filling frame and a pattern plate with a pattern thereon shutting off the mold chamber and onto which the mold making material is loosely heaped prior to compaction, and a valve placed between the pressure vessel and the mold chamber, the moving member of the valve opening (i.e. freeing the opening cross section of the valve) predominantly under the effect of the pressure in the pressure vessel.
An apparatus of the aforementioned type is disclosed in, for example, U.S. application Ser. No. 453,093, now U.S. Pat. No. 4,524,310, wherein the process for compacting mold material, more particularly in the form of foundry sand, made use of gas under pressure, as, for example, air under pressure or of gas pressurized by explosive combustion, the violent impact effect of which is such that the gas expanded out of a pressure vessel into the mold chamber to take effect on the free surface of the mold material causing compaction thereof by mutual exchange of momentum and by the deceleration of the mass of foundry material after it had first been accelerated on the top side of the pattern and the pattern plate. Furthermore, there were fluidizing effects and a concomitant decrease of friction between the particles. In the above mentioned patent, it was important to get a high mass flow of the gas and the highest possible rate of increase in pressure in the mold chamber. The lower the starting pressure in the pressure vessel, the higher these parameters had to be. The starting pressures were within the pressure range of commercial plant compressed air supplies in order to reduce costs, for the provision of the compressed gas and for the pressure control systems. Thus, the apparatus had to be fitted with a valve member capable of shutting down the largest possible cross section used for the transfer of the gas under pressure, and had to have a very low mass to make it possible for the cross section to be opened or uncovered in the shortest possible time or as instantaneously as possible. Furthermore, it was necessary to have valve opening drives capable of moving the valve member in a few milliseconds into the opened position to clear the flow path through the valve. It is not possible to meet these conditions using a normal commercial valve.
The above noted U.S. patent proposed some possible forms of valve design to maintain the desired conditions. Thus, for example, the gas under pressure was used at least for initiating or triggering the opening stroke of the valve so as to provide the most rapid possible equalization of pressure on the two sides of the valve member and so that any further opening motion of the member did not have to take place against the pressure effect. In all these designs the valve member was placed that it was moved directly into the pressure vessel, something which, in turn, made a special design of the valve member necessary.
Based on the above noted patent, utilizing the pressure gradient between the pressure valve and the mold chamber for opening the valve, an object of the present instant invention resides in providing an apparatus wherein the opening of the flow cross section is effected solely by the action of the gas under pressure.
In accordance with the present invention, the valve member is guided within the pressure vessel and an opening motion thereof is mainly directed into the mold chamber.
In the apparatus described in the above noted patent, the valve member is located wholly within the pressure vessel and opened therein however, in the present invention, the valve member is opened in the direction of the flow of the gas under pressure transferring into the mold chamber, thereby providing for a more effective way of working, and simpler means for maintaining the valve member in a closed position.
In accordance with the present invention, the valve member includes a valve plate having a plurality of openings formed, for example, by slots, with the plate cooperating with a stationary plate placed over it and between the pressure vessel and the mold chamber. The stationary plate includes openings such that the openings in the valve plate and in the stationary plate are out of line with each other so as to provide a gas-tight sealing effect. Furthermore, the valve plate is locked in the closed position by a locking means such that when it is unlocked it is accelerated by the gas under pressure into the mold chamber.
The valve plate and the stationary plate are formed as a sort of grating so designed that in the closed position the openings in the two plates do not overlap each other. That is to say, the openings in the stationary plate are closed by the valve plate and the holes in the latter are closed by the stationary plate. As soon as the least downward motion of the valve plate has taken place, the gas under pressure flows through the openings in the stationary plate and in the valve or moving plate into the mold chamber. Thus, for the expansion of the gas under pressure into the mold chamber, the valve member only has to be shifted through a very small distance to uncover or free the largest possible flow cross section.
Because, as a rule, flasks and filling frames are generally rectangular, it is best for the valve to have a rectangular form corresponding to the rectangular cross section of the mold chamber in order in this respect as well to get the maximum open or flow cross section and an equal distribution of the gas under pressure over the surface of the mold material.
In order to be certain of producing a hermetic seal in the closed position of the valve, the valve plate or the stationary plate are surfaced with a sealing layer on adjacent faces thereof, with the sealing layer extending around all the holes in the plate. More specially, the sealing layer is fixed to the valve plate rather than on a counterpart thereof.
In accordance with further features of the present invention the valve member is constructed as a thin valve diaphragm of a flexible material, that closes the opening between the pressure vessel and the mold space or chamber, with the valve member being sealingly locked in position at its edge when the valve is shut and, when unlocked and acted upon by the gas under pressure, sweeps inwards and downwards into the mold chamber.
The valve diaphragm may, for example, be made of rubber, a resin having the elastic properties of rubber, or of a resin with other elastic properties, with the only important factor being that the cross section of the material and the properties thereof are such that, when the edge of the valve diaphragm has been unlocked and it is acted upon by the gas under pressure, it swept or flapped as rapidly as possible into the mold chamber under the action of the gas under pressure and so uncover the maximum possible cross section of the opening. In this case as well the opening motion is caused solely by the action of the gas under pressure after the edge of the valve diaphragm has been unlocked.
By virtue of the above-noted features of the present invention it is possible for the opening between the pressure vessel and the mold to match the free cross section of the mold chamber, the valve diaphragm taking up, in the closed condition of the valve, a position within the pressure vessel such that its edge is placed on the floor part thereof around the opening. Because of the large opening cross section then made possible and the sudden opening of the cross section by the folding back of the valve diaphragm, the desired mass flow of gas and the sudden increase in pressure within the mold chamber may be produced very simply.
The flexible valve diaphragm may be maintained in the closed position by a loading ring or frame, that acts on its outer edge and is controlled by a locking and unlocking system. This ring or frame, that is also acted upon by the effect of the gas under pressure, forces the valve diaphragm against the pressure vessel floor round the opening. The loading ring or frame may be made with a relatively small mass so that only a small driving force is needed to lift it clear and start the opening motion of the valve diaphragm.
As a further part of a preferred form of the invention the material that the valve diaphragm produces a restoring force tending to move the valve diaphragm back into a position generally answering to the closed position. The valve diaphragm, that by virtue of the elastic nature is thereof forced into the mold chamber when the valve is opened, and will return to a straightened position by itself when the pressure is equalized and will go into a position, in which it is again within the pressure vessel and may be forced into contact at its edge by a closing drive that acts on the loading ring or frame.
In the case of this form of the invention there is the further feature that the valve member is mounted on a middle guide rod, by way of which it may be moved out of the valve-open position into the shut position, and by way of which a clamping device, responsible for the locking effect, may be locked in the closed position of the valve member.
This being so, the valve plate may be moved by the guide rod out of the open into the closed position. Then the guide rod is locked by the clamping device so that the pressure vessel may be filled with the gas under pressure. By releasing the clamping device, the valve plate will be freed and the pressurized gas acting on it will violently accelerate it into the open position. The clamping device forming part of the present invention with its radial action on the guide rod gives the useful effect that to release it only a very small displacement is required and consequently such displacement will be completed in a very short period of time and will be more or less instantaneous.
The closing drive for working the valve member may be in the form of a fluid pressure actuator acting on the guide rod and which after the guide rod has been gripped by the clamping device is unjoined from the guide rod, at least at the commencement of the opening motion. Subsequently, the driving connection is restored and the valve plate is moved back into the closed position by the guide rod.
If the valve plate is fabricated from a flexible material as a diaphragm, the ring or frame, designed to press on the edge of the valve diaphragm plate, will be mounted on the lower part of a two-part guide rod, whose lower part is guided so that it may slide to a limited degree in relation to the top part in the axial direction. The ring or the frame has springs for storing energy and which are rested against the edge of the opening and are tensioned when the valve is being closed, whereas, after the clamping device has been released, such springs accelerate the ring or frame upwards with the lower part of the guide rod, the valve diaphragm edge then being released. Under the effect of the gas under pressure the valve diaphragm is drawn out of the gap between the ring or frame and the floor round the opening of the pressure vessel and folds or flaps into the mold chamber.